In many processes, polyploid cells are generated by a variant of the normal cell cycle, called the endocycle, in which cells reduplicate their DNA without dividing. The transition from a normal mitotic cycle to the endocycle is poorly understood. In the December 2001 issue of Development, Professor Hannele Ruohola-Baker and colleagues report that this transition is regulated by the Notch pathway in Drosophila follicle cell epithelium. Loss of Notch in follicle cells, or of the Notch ligand Delta in the underlying germline, blocks the transition of follicle cells from the mitotic cycle to the endocycle. As a result, mitotic cycling continues and the cells overproliferate, becoming smaller than polyploid wild type cells. Regulation must occur at the transcriptional level because Suppressor of Hairless (Su(H)), a downstream transcription factor in the Notch pathway, is required for follicle cells to enter the endocycle. In the stage 12 egg chamber shown here, Su(H)SF8 mutant cells (lacking Green Fluorescent Protein or GFP) are smaller than wild type cells (green because of nuclear GFP). Armadillo staining (red) outlines the cell boundaries while DAPI staining of DNA (blue) labels all cells. The data demonstrate that Suppressor of Hairless (Su(H)) is required for follicle cells to exit the mitotic cycle.

The complete story can be found in Deng WM, Althauser C, and Ruohola-Baker, H. (2001) Notch-Delta signaling induces a transition from mitotic cell cycle to endocycle in Drosophila follicle cells. Development 128, 4737-4746.